The present invention relates to an optical disk device which reads and replays data recorded upon an optical disk such as a DVD or the like.
In the prior art, optical disk devices which read and replay data recorded upon optical disks such as DVDs or the like are per se widely known and very popular. As is per se well known, such an optical disk device irradiates laser light upon the recording surface of an optical disk, and reads the data which is recorded upon that optical disk by detecting the light reflected therefrom. In such an optical disk device various types of servo control are performed when reading data from the optical disk, such as rotational speed control of the optical disk (rotational speed control of the spindle motor), control for condensing the laser light irradiated towards the optical disk onto the recording surface of the optical disk (so called focus control), control for irradiating the laser light which is irradiated upon the optical disk into the center of the track from which the data is being read (so called tracking control), and the like. In an optical disk device, there is included a servo control unit which generates, from the light which is detected after having been reflected from the optical disk, servo signals which are used for drive control of the spindle motor, the pickup head, an objective lens included in this pickup head, and so on. Moreover, there are provided various types of driver which drive the spindle motor, a thread motor which shifts the pickup head, and an actuator which supports the objective lens, based upon the servo signals generated by the servo control unit.
Since this servo control uses servo signals which, as described above, are created from the light which has been detected after being reflected from the optical disk, it becomes unstable if it experiences an influence when starting operation, or due to extraneous light. Proposals for preventing the occurrence of erroneous operation of the servo mechanism at such times when the drive units cannot be adequately driven are put forward in Japanese Laid-Open Patent Publication H05-62230 and Japanese Laid-Open Patent Publication H06-325396.
However, with a conventional type of optical disk device, the power supply which supplies operating power to the servo control unit which generates the servo signals, and the power supply which supplies operating power to a logic control unit which commands the drivers which drive the motors and actuators or the like whether or not to stop driving the pickup head and the objective lens, are different power supplies. Due to this, during replay of an optical disk or the like, if the user has mistakenly pulled out the AC cord or the like, due to the characteristics of the two power supplies, a difference arises between the rate of decrease of the voltage of the supply of operational power to the servo control unit, and the rate of decrease of the voltage of the supply of operational power to the logic control unit. As a result, sometimes the situation occurs that the servo control unit cannot operate in an adequate manner, before the logic control unit issues a command for stopping the drivers driving the pickup head and/or the objective lens. In other words, it may happen that, before the voltage of the supply of operating power to the logic control unit decreases to less than or equal to a voltage which can operate this logic control unit in an adequate manner, the voltage of the supply of operating power to the servo control unit decreases to less than or equal to a voltage which can operate this servo control unit in an adequate manner. Since, in this case, the logic control unit does not command the drivers to stop driving the pickup head and the objective lens, irrespective of whether or not the servo signal which is generated by the servo control unit is an improper signal, accordingly the drivers continue to drive the pickup head and/or the objective lens based upon an improper servo signal which is generated by the servo control unit, so that there has been a problem of inviting failure of the main part of the optical disk device.
The object of the present invention is to provide an optical disk device with which the reliability is enhanced by a command being rapidly issued to the driver to stop driving of the pickup head and of the objective lens, when a situation occurs in which the power supply to a servo control unit which creates a servo signal cannot be performed in a normal manner.